Well, right off the bat.....
1] It does sound like the RF aerial or your location is affecting TV reception and causing the No signal condition. There's a lot that can affect that. Distance from transmitter, whether the home is blocked by a hill or a forest between the transmitter and your home. The Height of the Aerial in relation to the transmitter, and hills and trees.
Distance -- the farther away you are, the more likely an RF amp is required to amplify the signal.
Concrete and steel buildings. If your located closer to them, they can act as a shield, blocking or lowering the signal intensity.
2 Viera Tools. It seems that most Viera Tools are activated by what you are watching at the present time.
If you record on the TV's recorder, a Viera Tool will activate when you are watching a recording on your TV. It doesn't activate if you're watching something on the Humax.
If your Humax or you have an Audio amp or DVD player connected to the TV set, and it's got the capability of making the TV turn itself on when you push the power button on the unit, or it's remote (that's a key point with the Humax, you'd need to press the power button on the Humax box for 100% verification) -- Then That box has CEC enabled control that Panasonic has named VIERA LINK.
If one of the box's ORIGINAL remotes can control the TV set's operations, then it's likely to have Viera Linked capabilities, and the Viera Tools button would then activate allowing you to access the Viera Link tools.
Overall....if there's nothing that makes the Viera Tools button open, it's more likely that the equipment that you're watching doesn't have a "special feature tools" that require access to them.
Take a look at possible tools available --
Just in case the picture above disappears --
I may need more clarification about the Humax remote and the Viera Tools access. I could understand if the Humax remote was programmed to also operate the TV's Power and Volume controls, maybe even the TV menu versus the TV tools....but that's an awfully well programmed Humax remote if you can actually access the Tools while watching the Humax.
Turning the TV on and off, and adjusting volume is pretty basic for any remote to do.
But Viera Tools....only the TV remote needs to do that. But if Humax put that programming into their remote, that's quite impressive of them.